Randomized trial of total parenteral nutrition in critically ill patients: metabolic effects of varying glucose-lipid ratios as the energy source

Abstract

We studied 20 critically ill patients receiving ventilatory support to determine both their metabolic requirements and the effect of providing energy substrate regimens containing different lipid to glucose calorie ratios on whole-body protein economy. The measurements used included indirect calorimetry, substrate hormone profile, and whole body protein turnover by [14C]leucine. Measurements were done while patients were receiving all their nonprotein calories as dextrose ( D100 ) and were compared with results obtained when they received all their nonprotein calories as a combination of dextrose and lipid in a calorie ratio either of 3:1 ( D75 ) or 1:3 ( D25 ). To maintain euglycemia, exogenous insulin was infused by attending physicians not cognizant of the total parenteral nutrition regimen used. Energy expenditure before receiving total parenteral nutrition was only 4.6% above basal, and did not rise significantly during any of the regimens. The insulin infusion rate, plasma insulin, CO2 production, and serum lactate were significantly higher with D100 than with D25 , but not with D75 . Correspondingly, plasma free fatty acids were significantly lower with D100 when compared with D25 but not with D75 . Despite this, there were no significant differences in whole-body protein synthesis, breakdown, or net synthesis (synthesis - breakdown) and, in general, the patients in all groups were close to zero protein balance. These data suggest that critically ill patients are not severely hypermetabolic, and that they can maintain protein balance with a modest excess of calories while using a wide range of fuel mixtures.